Lake Petenwell is an artificial lake on the Wisconsin River in central Wisconsin. It is located in Adams, Juneau, and Wood counties next to Castle Rock Lake. It covers over 23,000 acres (93 km) and is 42 feet (13 m) deep.

Lake Petenwell is Wisconsin's second largest lake at 23,040 acres (93.2 km) or approximately 36 square miles (93 km). It was created in 1948 by the Wisconsin River Power Company with the construction of a dam across the Wisconsin River near Necedah. It has a maximum depth of 42 feet (13 m) and is used for skiing, sailing and fishing. Private lakefront property is very limited as most of the virgin shoreline is undeveloped forest. Wildlife includes wintering bald eagles. Game fish include walleye, northern pike, bass, panfish, and muskellunge.

The area around the lake has restaurants, a community theater, a golf course and two casinos.

Blue-green algae was reported in the lake in 2013. In 2019, Adams County website stated that the beaches were not closed due to algae, and that the situation was being monitored.

• Petenwell Castlerock Property Owners Association Archived 2012-01-29 at the Wayback Machine
• Wisconsin Dept of Natural Resources
• Petenwell County Park
• Petenwell Grand View Shores Association